Surgical procedures can require gases or other fluids to be injected into a target area for treatment of certain injuries, disorders and diseases. In the treatment of eye conditions such as macular holes, retinal tears and detachments, part of the surgical procedure can include the injection of gases or other fluids into the eye.
For example, retinal detachment is an eye disorder involving the separation of the retina from the Retinal Pigment Epithelium (RPE), the tissue that holds the retina in place. Retinal detachment can occur due to a retinal tear, traction on the retina, or inflammation which allows fluid to build up in the subretinal space thereby causing the retina to begin to separate from supporting RPE tissue. This disorder can also occur due to Posterior Vitreous Detachment (PVD), Proliferative Diabetic Retinopathy (PDR), injury, or neovascularization of the fibrous or vascular tissue causing the retina to be detached from the RPE. Such a condition, if not treated immediately, could lead to partial vision loss and potentially even blindness.
Treatment approaches for uncomplicated retinal detachments may include non-surgical techniques such as pneumatic retinopexy, laser photocoagulation, or cryopexy. More complicated retinal detachments require surgical intervention. Due to the risk of infection, which can potentially cause blindness, such surgeries are performed under sterile conditions in order to significantly reduce the potential for infection. Surgical methods include vitrectomy, which is the removal of the vitreous humor; dissection and removal of membranes, in the case of traction retinal detachments; and photocoagulation or cryopexy, in the case of additional retinal tears. Following such a surgical procedure, an intraocular gas tamponade may be used to hold the retina tissue in contact with the RPE which enables the retina to remain attached during the healing process after the surgical procedure.
Since intraocular pressure must be maintained relatively constant during the healing process, the gas chosen is typically one that expands at constant pressure (isobaric process). As such, the intraocular gas tamponade can be a gas bubble of air mixed with an expansile gas such as sulfur hexafluoride (SF6), hexafluoroethane (C2F6), or octafluoropropane (C3F8). The intraocular gas tamponade dissolves over time depending on the gas and concentrations used. For example, sulfur hexafluoride dissolves within 1-2 weeks when mixed with air at a concentration of approximately 20 percent, hexafluoroethane dissolves in approximately 4-5 weeks when mixed with air at a concentration of approximately 16 percent, and octafluoropropane dissolves in approximately 6-8 weeks when mixed with air at a concentration of approximately 12%. Changing the concentrations of these gases affects the duration.
Current practice involves use of gases contained in separate, multi-dose pressurized containers which are then transferred into a syringe for mixing with air and injection into the patient's eye. Therefore, during a surgical procedure, multiple non-sterile and sterile steps are required in order to fill the syringe with a desired concentration of gas and air. These non-sterile and sterile steps are typically performed by the non-sterile operating room circulating nurse and the sterile scrub technician supporting the surgeon in the sterile field. During a first non-sterile step, the circulating nurse prepares the non-sterile re-usable gas container by setting a pressure regulator connected to the gas container at the proper pressure. During a second step, the scrub tech prepares a sterile syringe by connecting a stopcock, filter, and tubing, in series, onto the syringe. During a third step, the tubing is connected to the gas container. The scrub tech carefully passes the free end of the sterile tubing through the invisible sterile barrier to the awaiting non-sterile circulating nurse. The non-sterile circulating nurse receives the tubing and carefully ensures that he/she does not contaminate the scrub tech nor any other of the sterile surfaces; and connects the tubing to the regulator on the gas container. During a fourth step, the syringe is then filled with gas from the container. The scrub tech and circulating nurse coordinate the opening of the pressurized container valve to release gas through the connected tubing, filter, stopcock, and into the syringe. The pressure of the released gas is sufficient to push the syringe plunger along the length of the syringe barrel and thus fill the syringe with gas. The scrub tech ensures that the gas does not push the plunger out of the open end of the syringe barrel and signals to the circulating nurse to close the gas container valve when the syringe approaches a fully filled condition. During a fifth step, the syringe is then purged of all air and gas in order to ensure that a substantial majority of air which may have been present within the syringe, stopcock, filter, and tubing, prior to filling with gas has been purged. The scrub tech turns the stopcock, to provide a means for the air and gas in the syringe to be released to the atmosphere, presses on the syringe plunger, and empties the syringe of all of its contents. The scrub tech then turns the stopcock in the opposite direction, returning the connection pathway to the tubing and the gas container. Steps four and five are repeated several times to further reduce the amount of air that was initially in the syringe, stopcock, filter, and tubing; flushing the majority of the air from the syringe, stopcock, filter, and tubing and purging the system of air. During a sixth step, the syringe is then refilled with gas from the container. The scrub tech detaches the tubing from the filter and signals the circulating nurse to carefully take the tubing, removing it from the sterile field. During a seventh step, the scrub tech does not expel the full contents of the syringe, stopping the plunger such that only a measured volume of gas remains in the syringe. For example, the gas may be expelled such that only 12 mL remains within the syringe. During an eighth step, the scrub tech replaces the used filter with a new sterile filter and draws filtered room air into the syringe until the total air/gas mixture in the syringe is at a proper volume for the desired gas concentration.
For example, atmospheric air may be drawn into the syringe such that the total volume of air and gas is 60 mL therefore achieving a concentration of 20 percent. Since the pressurized containers are non-sterile, and the syringe and surgical area are sterile, completing the above-mentioned steps must be performed by at least one party in the non-sterile field (typically the circulating nurse), a second party in the sterile field (typically the scrub tech), and requires the coordination and communication between the two parties.
The procedure requires a complex set of steps which may increase the potential for errors occurring. An error in one of these steps can result in an improper concentration of gas being used which may result in having either an elevated pressure or reduced retinal tamponade duration thereby potentially causing ischemia or failure of the reattachment surgery, both of which potentially causing blindness. Additionally, the current practice results in a significant amount of wasted gas which is both expensive and harmful to the environment. Thus handling of such gases, especially in pressurized containers containing more than one dose, may present potential danger to the operator if mishandled. As such, some countries may even prohibit storage of these pressurized containers in the operating room.
While there have been some approaches to improve the current procedure, such as U.S. Pat. No. 6,866,142 to Lamborne et al., single-dose containers capable of being placed in the sterile field, and the Alcon® Constellation® system which allows filling and purging of gas, these approaches have been insufficient to address all the potential issues. As such, there remains a need in the industry for an improved gas mixing apparatus.